How does a exhaust valve of auxiliary engine rotate ? How does the main enigne exahast valve rotate?

Rotocap Working....!!!

ROTOCAP

PURPOSE OF ROTOCAP.
The rotocap is a mechanical means to rotate the valve unlike the main engine exhaust valves which has got vanes in it...

The rotocaps are usually fitted tot the exhaust valves, this ensures that the valve rotates and inturn ensures that the valve is kept at an even temperature so it does not distort and helps in even distribution of carbon deposits.

 CONSTRUCTION AND WORKING.

                              There is a collet or cotter which is on the valve cover fitted around the exhaust valve. The valve cover has number of inclined tracks machined into it. Each contains a ball and a spring. The balls runs on the race. Now when the valve is closed, the belville washer locks the valve cover and the spring carrier together preventing rotation, and at the same time acts on the ball race, pushing it hard up against the balls, locking them half way up the inclined track and compressing the springs.

                               As the valve starts to open, the increasing valve spring force cause the belville washer to flatten. The ball race no longer locks the balls in the inclined tracks and therefor the valve cover is free to  move. The valve cover now moves over the ball bearings until the balls are at the end of inclined tracks, as the cover rotates, so does the collet and the valve spindle.

                               

                                 As the valve shuts, the belville washer locks the valve cover to the spring carrier and applies pressure to the ball races as mentioned above and forces balls back up the inclined tracks and locking them up preventing rotation.

FACTS 

1.  Rotocaps stop operating below about 25 % of engine load.
2. Contaminants in the lube oil which lubricates the valve gear may cause deposits in the inclined tracks and makes the rotocap ineffective..
3. It should be noted that rotocaps rotate the valve as it opens and not when it closes as it is in the main engine exhaust valve.

MAIN ENGINE EXHAUST VALVE WORKING.

The main engine exhaust valve has vanes fitted to them just above the head of the valve, which help in rotation of the exhaust valve.

The high velocity exhaust gases acts on these vanes and then the valve rotates while closing.

Exhaust valve fitted with VANES.